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Characters of Growth and Ethanol Production of a Candida Tropicalis Yeast in Xylose Fermentation

Author: LiuLanJie
Tutor: GeXiangYang
School: Huazhong Agricultural University
Course: Fermentation Engineering
Keywords: Candida tropicalis xylose ethanol fermentation productivity rate of conversion
CLC: TS262.2
Type: Master's thesis
Year: 2010
Downloads: 65
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Abstract


Xylose is the major pentose components of the hydrolysis of cellulosic materials.In nature, the microorganism which can metabolize and use xylose is rare, especially yeast. The few yeast which is able to assimilate xylose produce ethanol or single cell protein (SCP) efficiently. Therefore, the breeding of strains which can use xylose efficiently is one of the keys of the development and utilization of renewable resources cellulose, as well as the research of the xylose fermentation characteristics about those strains.A new isolated strain candida tropicalis strain 3#was employed in this study. In this study, the xylose fermentation characteristics of strain 3# were studied, including both of the production of ethanol and SCP and the Initial exploration about practical application of strain 3#. Results were as follow:1. To the strain 3#, the characteristics of xylose fermentation about ethanol production ware studied, The results indicated that, the dissolved oxygen(DO) concentration had a significant impact on both of yield and productivity of ethanol, and the moderate dissolved oxygen concentration was conducive to the accumulation of cell growth and ethanol. Higher initial cell concentration and urea promoted the production and accumulation of ethanol. What’s more, in the case of sufficient carbon and nitrogen, to extend the fermentation time, ethanol production was up to 25.58 g/L in the steady state, as well as cell growth was also stabilizing with the concentration of 6.54×108/mL. This steady state was dynamic equilibrium, which was due to that the production was consistent with the consumption of ethanol.2. To the strain 3#, the characteristics of xylose fermentation about SCP production were studied, The results indicated that:the SCP production cycle of xylose fermentation of strain 3# was 48 h.When the initial xylose concentration of xylose was 1% in the culture medium, the rate of conversion was higher about 35.7%, but the cell concentration increased with the augmentation of the xylose concentration. The utilization of soybean meal as nitrogen source could get the highest cell concentration, which was 7.25 mg/mL. Different fermentation temperatures had an obvious impact on the growth and conversion of cell, and under the temperature of 30℃there was the highest cell concentration, which was 8.01 mg/mL, while the highest yield was up to 51.9% at 25℃. DO made a great impact on cell growth, and sufficient oxygen supply was an important prerequisite for getting high concentration and conversion rate of cell. When the inoculation was 5%, the rate of conversion was the highest which was 52.5%, but when inoculation was 20%, the cell concentration was the highest which was 9.9 mg/mL. When the way of feeding of xylose was 2%+3%+3%, the rate of conversion was the highest which is 46.6%, but when it was 3%+2%+3%, the cell concentration was the highest, which was 15.5×109/ml.3. The preliminary research of practical application about the fermentation of cellulosic material hydrolyzate had been done. And the results indicated that:the reducing sugar concentration of the corncob hydrolyzate could reach to 40 g/L, which satisfied the conditions of xylose fermentation to produce ethanol or SCP. In this experiment, ethanol and SCP were produced in different conditions. Loaded 100 mL corncob hydrolyzate in 250 mL flask, and then fermented to produce ethanol for 3 days. The reducing sugar concentration of the fermentation broth was 20.34 g/L, with the yield of ethanol 3.46 g/L. Similarly, loaded 50mL corncob hydrolyzate in 500 mL flask, and then fermented to produce SCP for 48 hours. The cell concentration of the fermentation broth was 780 million/mL, and the reducing sugar concentration was 5.48 g/L. So this strain 3# has certain practical value for cellulose hydrolyzate fermentation.

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